1. Field of the Invention
The present invention relates to mechanical reverberation apparatus artificially constructed and adapted to produce acoustic effects similar to those occuring spontaneously when sounds are transmitted in a partly or completely enclosed room or in a space bounded by walls reflecting the acoustic waves.
More specifically, the invention relates to reverberation units adapted to be inserted between a) an electro-mechanical driver transducer receiving sound-frequency electric input signals produced by a microphone connected to an amplifier and converting them into mechanical vibrations and b) a mechanical to electrical pick-up transducer receiving the aforesaid mechanical vibrations and producing an output of new sound-frequency electric signals having a different wave shape from the input signals, solely as a result of the multiple reflections undergone by the vibrations in the so-inserted reverberation units. The new electric signals can of course be used, after amplification if necessary, for energizing a loudspeaker or similar device.
2. Description of the Prior Art
In the prior art, reverberations are produced by suitably converting a sound-frequency electric signal to a plurality of sound frequency signals. A signal, which is the electric equivalent of a sound, is hereinafter called the input signal. Thus an artificial reverberation system or device converts a number of input signals simultaneously to output sound frequency signals. For simplicity, only a single input signal will be mentioned except in special cases.
The term "reverberation unit" is used to define a system or device for artificially producing reverberation effects from a sound-frequency input electric signal. From an input signal the reverberation unit provides a plurality of outputs of sound-frequency electric signals which energize loudspeakers or headphones and produce the desired acoustic reverberation effect.
It is also known that a mechanical reverberation unit of the coiled spring type provides an artificial reverberation effect. The known unit comprises a plurality of coiled springs used as a transmitter of mechanical sound vibrations and are aligned into one or several systems all parallel to a common axis or direction. Such a reverberation unit with a coiled spring system is exemplified in U.S. Pat. No. 3,106,610 filed on Jan. 30, 1961. The system described in this patent comprises a plurality of coil springs individually mechanically coupled at one end to movable elements of a first transducer and at the other end to movable elements of a second transducer. The coil springs are supported solely therebetween in parallel positions by their connections to said movable elements. The mechanical vibrations are provided by means of a first transducer as an electromechanical driver via the corresponding movable elements which are energized when the input terminals of the first transducer receives a sound-frequency signal. The second transducer serves as a mechanical-electric pick-up and is energized by the mechanical vibrations to generate to its output terminals an electrical signal whenever its movable elements are vibrated.
Owing to the low coupling characteristic between a coil spring and transducer or at the most two coil springs and the connections of ends of each aligned coil spring system with the movable elements of the transducers, mechanical mismatches are very frequent between the systems and the transducers. Since the number of coil springs is relatively small, the mechanical characteristics of the component elements, such as coil springs must necessarily be made very exact. However, the reverberation unit, due to these characteristics, is sensitive to output vibrations and thereby introduces some inherent distortion from the coil springs. The relatively low efficiency of these reverberation units which results from the prior art design limits the usefulness and also such operating characteristics as the reverberation time.